Every biography and history book about the Apollo program I've read mentions people working long hours during the lead-up to the moon landing. I have can't think of a source that gave a specific number of hours, but they all agreed that working late and working on weekends was extremely common.

Nothing I've read ever mentioned anything about union concerns. I don't think that the white collar workforce at NASA has ever had a union, but I cannot say that for sure.

Apollo wasn't the sort of program you worked on because you wanted a nine to five job. Go Flight! is a pretty decent book about the history of Flight Operations (mission control) at NASA, and it talked about how people knew perfectly well what they were signing up for when they took NASA jobs back then. There were jobs that paid more money with shorter hours in private industry, and anyone who was smart enough to work as an engineer or manager for NASA could have gotten hired somewhere else. As a group (obviously there are always individual exceptions) people worked for the space program because they cared about what it was doing, not because it was the most comfortable job available.